Why can't we use the middle button of a Venu 3 in our CIQ apps?

Hello,

I will soon get a Venu 3 and I noticed it has a third button in the middle that my Venu 2 doesn't have.

I read that this is a shortcut button where I can open an app or a training mode quickly, and that alone sounds very useful.

However, I also have some personal apps I developed myself for my Venu 2. 

One of these apps could greatly benefit from the third button as I could then navigate and control the entire app using just the buttons and wouldn't have to rely on the touchscreen that sometimes (e.g. with wet fingers or with thicker gloves on) doesn't work or produces false inputs.

I then tried to find out the ID of this button by writing a BehaviourDelegate that contains this:

function onKey(evt) {
    var key = evt.getKey();
    System.println(key);
    return false;
  }

I ran it on the simulator and it printed the correct button IDs for the "old" two buttons that the Venu 2 also has, but there was no output at all for the middle button.

I then researched a bit and found this:

https://developer.garmin.com/connect-iq/device-reference/venu3/

https://developer.garmin.com/connect-iq/device-reference/venu2/

Where it says for the Venu2:

Buttons: enter, menu, esc

and the same for the Venu 3...

So is the third (middle) button on the Venu 3 just reserved by the system and not usable in our own apps?

Thanks in advance

Aaron